The atmosphere is being presently overburdened by carbon emissions produced from fossil fuels. The burning of fossil fuels presently contributes to an annual release of 4 billion metric tons of carbon dioxide into the atmosphere and the injection of 2 billion metric tons of carbon dioxide into the world's oceans. It has been well documented that these carbon emissions negatively impact living organisms in the oceans as well as on land. It is desirable to minimize the impact of the fossil fuel emissions.
There is presently interest in producing biofuels from a wide variety of feedstocks, in order to provide suitable replacements for fossil fuels. There is also interest in reducing the carbon footprint of many industrial processes. By carbon footprint of a conversion process is meant the emissions of greenhouse gases generated by the conversion process. It is generally expressed as amount of carbon dioxide equivalents per weight of produced product or produced energy. Carbon dioxide is the primary greenhouse gas considered, although any other greenhouse gases such as nitrogen oxide and methane falls under the category. The carbon footprint generally entails production and consumption of food, fuels, manufactured goods, and materials and services used in the conversion process.
In particular, it is desirable to reduce the carbon footprint of a carbon positive process, or combine any carbon positive process or processes with one or more negative carbon processes to reduce the carbon footprint of a given process. The idea of carbon negative processes in the production of fuels has been previously discussed. See, for example, J. A. Mathews, “Carbon-negative biofuels”, in Energy Policy 36 (2008) pp. 940-945.
Approaches directed toward the production of carbon negative fuels include those described in US Patent Publication 2010/0311157, which teaches the production of biofuels from algae as feedstock. The process is claimed to be carbon negative due to the high absorption of CO2 by the algae. US Patent Publication 2010/0040510 discloses a multistage pressurized fluidized bed gasifier operating between 780° C. and 1100° C. that converts biomass to synthesis gas and biochar. The biochar is said to be capable of being added to soil. The formation of methane, gasoline-like volatiles such as BTX (benzene, toluene, and xylene) and tar is explicitly avoided. The gasifier is said to possibly produce carbon negative fuel. US Patent Publication 2008/0317657 discloses a system and method for sequestering carbon in the form of char created by gasifying biomass in an unspecified reactor vessel. A low heating value producer gas is a by-product of the process. US Patent Publication 2004/0111968 discusses pyrolyzing biomass to produce char and pyrolysis gases which are steam reformed to hydrogen. The char is treated to become a carbon based fertilizer.